The subject invention is generally directed to swath type printers, and more particularly to apparatus and techniques for reducing pixel density to allow for higher resolution printing with print elements designed for lower resolution printing.
A swath printer is a raster or matrix type printer that is capable of printing a plurality of rows of dots in a single scan of a movable print carriage across the print media. The possible locations for dots that can be printed by a raster printer can be represented by an array or grid of pixels or square areas arranged in a rectilinear array of rows and columns wherein the center to center distance or dot pitch between pixels is determined by the resolution of the printer. For example, if a printer is capable of printing 300 dots per inch (dpi), the dot pitch of the pixel array would be 1/300th of an inch.
The print carriage of a swath printer typically includes a plurality of printing elements (e.g., ink jet nozzles) displaced relative to each other in the media motion direction which allows printing of a plurality of rows of dots. The separation between the printing elements in the media scan direction corresponds to the dot pitch for the finest raster row resolution that can be printed by the printer in a single carriage scan (e.g., 1/300th of an inch for 300 dot per inch (dpi) resolution). The printing elements of a swath printer are commonly implemented in a printhead such as a thermal ink jet printhead that is integral to a replaceable thermal ink jet printhead cartridge.
The quality of the printed images produced by a raster printer depends to large degree on the resolution of the printer. Higher or finer resolution wherein the printed dots are more closely spaced provides for higher quality images.
A consideration with increasing the resolution of ink jet printers is that increased resolution requires more printed dots per unit area, with the number of dots increasing by the product of the increase factor along each dimension. For example, doubling print resolution from 300 dpi to 600 dpi results in four times as many dots per unit area. Since the number of dots per unit area increases with resolution, the size of each printed dot must decrease with increased resolution in order to avoid saturating the print media. For example, if a 300 dpi ink jet cartridge were utilized to print at 600 dpi, the amount of ink per unit area would increase by a factor of four, just as the number of dots increased. However, the design and implementation of higher resolution ink jet cartridges with reduced dot size may be impractical, and moreover the use of a reduced dot size that is appropriate for the highest printing resolution of the printer may also present difficulties in printing at reduced pixel densities that would be conveniently utilized for increased throughput in those situations where the reduced pixel densities would be acceptable, such as drafts.